The present invention relates generally to the heat treating, sintering, or heating of refractory materials characterized by metal compounds such as oxides, nitrides, and sulphides by microwave energy and more particularly to the heating of such refractory materials in a microwave kiln or oven provided with a container which houses the material being heated and increases the efficiency of the microwave oven for concentrating microwave radiation on the housed material.
The utilization of microwave energy is receiving considerable interest for utilization in various refractory heating procedures since it is a relatively inexpensive source of heat and microwave radiation provides rapid and clean heating. The conventional microwave ovens or kilns utilized for heat treating various metal compounds such as oxides, nitrides, or sulphides have met with considerable success but yet suffer some shortcomings which detract from their overall effectiveness for heat treating or heating materials which are relatively poor susceptors or couplers of the microwave radiation so as to be slow in heating or even incapable of being heated to a temperature adequate for effecting the desired heating procedure on the material.
A significantly high loss of microwave radiation is normally encountered in the ovens presently available in that the heating of the material is effected by absorption of microwave energy by the material or a component of the material which functions as a susceptor for the microwave energy. Often the material does not contain sufficient microwave suscepting material to effect the heating thereof or is of a density which is less than that which will provide adequate coupling of the microwave energy as it passes through the article for obtaining the desired level of heating. This energy loss occurs when the microwaves miss the couplers or susceptors in the material as it passes therethrough. Energy losses also occur when the microwaves are passing through a region of the oven remote to the material. Efforts have been made to overcome these energy losses in conventional microwave ovens and include such practices as the employment of higher power levels and/or higher frequencies for heating the material to the desired high temperature. The provision of such higher power levels and/or frequencies is frequently unavailable for commercially provided microwave kilns or ovens and even if available are somewhat undesirable due to the poor economics of such ovens since the energy loss is even greater in these higher-powered ovens due to the increased number or energy level of the microwaves missing the coupling material in the solid compound being heated.